Pitzer Strain
In chemistry, a molecule experiences strain when its chemical
structure undergoes some stress which raises its internal energy in
comparison to a strain-free reference compound. The internal energy of
a molecule consists of all the energy stored within it. A strained
molecule has an additional amount of internal energy which an
unstrained molecule does not. This extra internal energy, or strain
energy, can be likened to a compressed spring.[1] Much like a
compressed spring must be held in place to prevent release of its
potential energy, a molecule can be held in an energetically
unfavorable conformation by the bonds within that molecule
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ChemistryChemistryChemistry is the scientific discipline involved with compounds
composed of atoms, i.e. elements, and molecules, i.e. combinations of
atoms: their composition, structure, properties, behavior and the
changes they undergo during a reaction with other compounds.[1][2]
ChemistryChemistry addresses topics such as how atoms and molecules interact
via chemical bonds to form new chemical compounds. There are four
types of chemical bonds: covalent bonds, in which compounds share one
or more electron(s); ionic bonds, in which a compound donates one or
more electrons to another compound to produce ions: cations and
anions; hydrogen bonds; and
Van der Waals forceVan der Waals force bonds
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Pentane InterferencePentane interferencePentane interference or syn-pentane interaction is the steric
hindrance that the two terminal methyl groups experience in one of the
chemical conformations of n-pentane. The possible conformations are
combinations of anti conformations and gauche conformations and are
anti-anti, anti-gauche+, gauche+ - gauche+ and gauche+ - gauche− of
which the last one is especially energetically unfavorable. In
macromolecules such as polyethylene pentane interference occurs
between every fifth carbon atom. This is not to be confused with the
1,3-diaxial interactions of cyclohexane derivatives (gauche
interactions shared between substituents and the ring). A clear
example of the syn-pentane interaction is apparent in the diaxial
versus diequatorial heats of formation of cis 1,3-dialkyl
cyclohexanes
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Heat Of Combustion
The heating value (or energy value or calorific value) of a substance,
usually a fuel or food (see food energy), is the amount of heat
released during the combustion of a specified amount of it.
The calorific value is the total energy released as heat when a
substance undergoes complete combustion with oxygen under standard
conditions. The chemical reaction is typically a hydrocarbon or other
organic molecule reacting with oxygen to form carbon dioxide and water
and release heat. It may be expressed with the quantities:energy/mole of fuel
energy/mass of fuel
energy/volume of the fuelThe calorific value is conventionally measured with a bomb
calorimeter. It may also be calculated as the difference between the
heat of formation ΔHo
f of the products and reactants (though this approach is purely
empirical since most heats of formation are calculated from measured
heats of combustion)
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Benson Group Increment Theory
Benson Group Increment Theory (BGIT) or Group Increment Theory or
Benson Group Additivity, uses the experimentally calculated heat of
formation for individual groups of atoms to calculate the entire heat
of formation for a molecule under investigation. This can be a quick
and convenient way to determine theoretical heats of formation without
conducting tedious experiments. The technique was developed by the
late Professor Sidney William Benson[1] of the University of Southern
California. It is further described in a separate Wiki page.
Heats of formations are intimately related to bond dissociation
energies and thus are important in understanding chemical structure
and reactivity.[2] Furthermore, although the theory is old, it still
is practically useful as one of the best group additivity methods
aside from computational methods such as molecular mechanics
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Van Der Waals Strain
In chemistry, van der Waals strain is strain resulting from van der
Waals repulsion when two substituents in a molecule approach each
other with a distance less than the sum of their van der Waals radii.
Van der Waals strain is also called van der Waals repulsion and is
related to steric hindrance.[1] One of the most common forms of this
strain is eclipsing hydrogen, in Alkanes.
In rotational and pseudorotational mechanisms[edit]
In molecules whose vibrational mode involves a rotational or
pseudorotational mechanism (such as the Berry mechanism or the Bartell
mechanism),[2] van der Waals strain can cause significant differences
in potential energy, even between molecules with identical geometry.
PF5, for example, has significantly lower potential energy than PCl5.
Despite their identical trigonal bipyramidal molecular geometry, the
higher electron count of chlorine as compared to fluorine causes a
potential energy spike as the molecule enters its intermediate in the
mechanism and the s
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Van Der Waals Radius
The van der Waals radius, rw, of an atom is the radius of an imaginary
hard sphere representing the distance of closest approach for another
atom. It is named after Johannes Diderik van der Waals, winner of the
1910 Nobel Prize in Physics, as he was the first to recognise that
atoms were not simply points and to demonstrate the physical
consequences of their size through the van der Waals equation of
state.Contents1 Van der Waals volume
2 Methods of determination2.1
Van der Waals equationVan der Waals equation of state
2.2 Crystallographic measurements
2.3 Molar refractivity
2.4 Polarizability3 References3.1 Further reading4 External linksVan der Waals volume[edit]This section does not cite any sources. Please help improve this
section by adding citations to reliable sources. Unsourced material
may be challenged and removed
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Butyl
In organic chemistry, butyl is a four-carbon alkyl radical or
substituent group with general chemical formula −C4H9, derived from
either of the two isomers of butane.
The isomer n-butane can connect in two ways, giving rise to two
"-butyl" groups:If it connects at one of the two terminal carbon atoms, it is normal
butyl or n-butyl: CH3−CH2−CH2−CH2− (fully systematic name:
butyl)
If it connects at one of the non-terminal (internal) carbon atoms, it
is secondary butyl or sec-butyl: CH3−CH2−CH(CH3)− (fully
systematic name: 1-methylpropyl)The second isomer of butane, isobutane, can also connect in two ways,
giving rise to two additional groups:If it connects at one of the three terminal carbons, it is isobutyl:
(CH3)2CH−CH2− (fully systematic name: 2-methylpropyl)
If it connects at the central carbon, it is tertiary butyl, tert-butyl
or t-butyl: (CH3)3C− (fully systematic name: 1,1-dimethylethyl)Contents1 Nomenclature
2 Example
3 Ety
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Methyl Group
A methyl group is an alkyl derived from methane, containing one carbon
atom bonded to three hydrogen atoms — CH3. In formulas, the group is
often abbreviated Me. Such hydrocarbon groups occur in many organic
compounds. It is a very stable group in most molecules. While the
methyl group is usually part of a larger molecule, it can be found on
its own in any of three forms: anion, cation or radical. The anion has
eight valence electrons, the radical seven and the cation six. All
three forms are highly reactive and rarely observed.[1]Contents1 Methyl cation, anion, and radical1.1 Methyl cation
1.2 Methyl anion
1.3 Methyl radical2 Reactivity2.1 Oxidation
2.2 Methylation
2.3 Deprotonation
2.4 Free radical reactions3
ChiralChiral methyl
4 Etymology
5 See also
6 ReferencesMethyl cation, anion, and radical[edit]
Methyl cation[edit]
The methylium cation (CH3+) exists in the gas phase, but is otherwise
not encountered
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Trimethylboron
Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula
B(CH3)3 (which can also be written as Me3B, with Me representing
methyl).Contents1 Properties
2 Preparation
3 Reactions
4 Use
5 ReferencesProperties[edit]
As a liquid it is colourless. The strongest line in the infrared
spectrum is at 1330 cm−1 followed by lines at 3010 cm−1
and 1185 cm−1.
Its melting point is −161.5 °C, and its boiling point is
−20.2 °C.
Vapour pressure is given by log P = 6.1385 + 1.75 log T − 1393.3/T
− 0.007735 T, where T is temperature in kelvins.[5] Molecular weight
is 55.914. The heat of vapourisation is 25.6 kJ/mol.[4]
Preparation[edit]
Trimethylborane was first made by Stock and Zeidler
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Herbert C. Brown
Herbert Charles Brown (May 22, 1912 – December 19, 2004) was an
English-born American chemist and recipient of the 1979 Nobel Prize in
ChemistryChemistry for his work with organoboranes.Contents1 Life and career
2 Research
3 See also
4 References
5 External linksLife and career[edit]
Brown was born Herbert Brovarnik in London, to Ukrainian Jewish
immigrants from Zhitomir, Pearl (née Gorinstein) and Charles
Brovarnik, a hardware store manager and carpenter.[2] He moved to
ChicagoChicago in June 1914, at the age of two.[3][4] Brown attended Crane
Junior College in Chicago, where he met Sarah Baylen, whom he would
later marry. The college closed soon after, and Brown and Baylen
transferred to Wright Junior College.[4] In 1935 he left Wright Junior
College and that autumn entered the University of Chicago, completed
two years of studies in three quarters, and earned a B.S
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Alkyl
In organic chemistry, an alkyl substituent is an alkane missing one
hydrogen.[1] The term alkyl is intentionally unspecific to include
many possible substitutions. An acyclic alkyl has the general formula
CnH2n+1. A cycloalkyl is derived from a cycloalkane by removal of a
hydrogen atom from a ring and has the general formula CnH2n-1.[2]
Typically an alkyl is a part of a larger molecule. In structural
formula, the symbol R is used to designate a generic (unspecified)
alkyl group. The smallest alkyl group is methyl, with the formula
CH3−. [3]Contents1 In everyday life
2 In medicinal chemistry
3
AlkylAlkyl cations, anions, and radicals
4 Nomenclature
5 Etymology
6 See also
7 ReferencesIn everyday life[edit]
The word root alkyl is encountered in several contexts.
AlkylationAlkylation is
an important operation in refineries, for example in the production of
high-octane gasoline
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PentanePentanePentane is an organic compound with the formula C5H12—that is, an
alkane with five carbon atoms. The term may refer to any of three
structural isomers, or to a mixture of them: in the IUPAC
nomenclature, however, pentane means exclusively the n-pentane isomer;
the other two are called isopentane (methylbutane) and neopentane
(dimethylpropane).
CyclopentaneCyclopentane is not an isomer of pentane because it
has only 10 hydrogen atoms where pentane has 12.
Pentanes are components of some fuels and are employed as specialty
solvents in the laboratory. Their properties are very similar to those
of butanes and hexanes.Contents1 Industrial uses
2
LaboratoryLaboratory use
3 Physical properties
4 Reactions
5 References
6 External linksIndustrial uses[edit]
Pentanes are some of the primary blowing agents used in the production
of polystyrene foam and other foams
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MethylcyclopentaneMethylcyclopentaneMethylcyclopentane is an organic compound with the chemical formula
CH3C5H9. It is a colourless, flammable liquid with a faint odor. It is
a component of the naphthene fraction of petroleum. It usually is
obtained as a mixture with cyclohexane. It is mainly converted in
naphthene reformers to benzene..[2]
MethylcyclopentaneMethylcyclopentane is not
perfectly planar and can pucker to alleviate stress in its
structure.[3]
References[edit]^ a b c Lide, David. R, ed. (2009). CRC Handbook of Chemistry and
Physics (89th ed.). CRC Press. ISBN 978-1-4200-6679-1.
^ M. Larry Campbell. "Cyclohexane" in Ullmann's Encyclopedia of
Industrial Chemistry, Wiley-VCH, Weinheim, 2012.
doi:10.1002/14356007.a08_209.pub2
^ Carey, Francis; Giuliano, Robert (2014). "3". Organic Chemistry (9
ed.). McGraw-Hill. pp. 97–131
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